7.5.16.5 SRFI-19 Date to string

Function: date->stringdate [format]

Convert a date to a string under the control of a format.
format should be a string containing ‘~’ escapes, which
will be expanded as per the following conversion table. The default
format is ‘~c’, a locale-dependent date and time.

Many of these conversion characters are the same as POSIX
strftime (see Time), but there are some extras and some
variations.